This application is based on and claims the benefit of German Patent Application No. 10151827.7 which is incorporated by reference herein.
The present invention relates to a process for continuous production of longitudinally welded metal tubing, in which a metal strip is withdrawn from a strip supply, gradually shaped into tubing with an open longitudinal slit, and the longitudinal slit is sealed by soldering or by welding at a welding point.
The continuous production of longitudinally welded metal tubingxe2x80x94either smooth or corrugatedxe2x80x94has been known for a long time.
The technical brochure entitled Uniwema-Maschinen und Zubehxc3x6r (Uniwema Machines and Accessories) by kabelmetal electro GmbH describes a process by means of which metal tubing with a diameter of 2 to 400 mm and a wall thickness of 0.05 to 4.0 mm can be produced in nearly infinite lengths.
In this process, a metal strip is withdrawn from a reel, possibly cleaned, shaped into slit tubing in a plurality of shaping steps on a shaping table, and the longitudinal slit of the tubing is welded in a welding unit. Behind the welding unit, the metal tubing is grasped by a so-called collet feed, which transports the metal strip and the metal tubing at a uniform speed. For this purpose, the collets, which are mounted on two endless roller chains, enclose the tubing. The collets are provided with jaws that are precisely adapted to the diameter of the tubing
The welded tubing is then usually wound onto a cable reel.
The problem with this prior-art process is that due to the shaping of the metal strip into the slit tubing and the welding of the longitudinal edges, tubing with an outside diameter of less than 2 mm can no longer be produced. To be able to produce tubing with a smaller diameter, the tubing must be reduced in one or several steps. This is accomplished by pulling the tubing through a die, the inside diameter of which is smaller than the outside diameter of the tubing to be reduced. If the wall thickness of the tubing is also to be reduced in this drawing process, a mandrel, the outside diameter of which is greater than the inside diameter of the die, must be inserted into the tubing.
To reduce friction between the tubing wall and the shaping tools (i.e., the die and mandrel), a lubricant must be added. Lubricating the tube from the outside presents few problems. It is difficult, however, to introduce the required amount of lubricant into the interior of the tubing, if the tubing lengths to be drawn are large.
In view of the above, an object of the invention is to define a process suitable for producing metal tubing of great lengths, which in a subsequent process step can be easily reduced both with respect to the outside diameter and the wall thickness.
This object is attained by a method as described above, further including the step of introducing a lubricant into the open slit tubing. The lubricant can be a lubricating oil introduced in drops behind the welding point, and may be introduced in an amount sufficient to coat the entire inner surface of the metal tubing.
The essential advantage of the invention is that it provides a simple method for coating the inner surface with a precisely metered amount of lubricant, so that the subsequent drawing process can be performed without difficulties, i.e. without damaging the inner surface of the tubing, and thus without risk that the tubing may tear off behind the die.